The a gas sensor, in particular a lambda probe, for ascertaining the pollutant and/or oxygen content in emission gases of internal combustion engines.
German Patent Application No. 42 04 850 describes a gas sensor which has a housing used for accommodating a sensor element. The sensor element has a section on the terminal side and a section on the measuring-gas side. Using a connecting element, the sensor element, having a plurality of electrically conductive contact areas, is connected at its terminal-side section to electrically conductive supply leads. The connecting element is composed of two sections held together by a sleeve, between which the sensor element and the supply leads are immovably retained. Because several parts are necessary for the connections of the supply leads to the sensor element, the assembly of the gas sensor, in particular the connection of the gas sensor to the supply leads, is costly. In addition, the production costs of the multi-part connecting element are high.
The gas sensor of the present invention, has the distinction that the connecting element is formed from a spring element produced in one piece from ceramic material. Because the spring element is designed in one piece, it can be produced very simply, and thus cost-effectively, using, for example, the extrusion method, therefore in just one procedure. The sensor element and the supply leads are frictionally connected to one another by the spring element which can be easily mounted. To that end, first the connectors are introduced into or extended through a feed-through opening of the preferably ring-shaped spring element, and the sensor element is subsequently fixed in position and retained by sliding on the spring element. Alternatively, it is also possible to insert the sensor element into the feed-through opening or optionally, to mount it by pressing. The assembly can be accomplished simply and quickly for both embodiment variants. The spring element makes it possible to realize a great contact force acting in the radial direction between the supply leads, the sensor element and the spring element. Due to the small mass of the spring element, the sensor element is only slightly dynamically stressed, i.e., in the event of vibration, only a small deflection takes place.
In one exemplary embodiment of the gas sensor, at least one slit is introduced into the feed-through opening of the spring element. This makes it possible to realize a great spring excursion of the spring element produced from ceramic material. When slipping the spring element onto the sensor element, or when inserting the sensor element into the feed-through opening of the spring element, the spring element is spread. This ensures that the supply leads will not be shifted, at least substantially, when forming the frictional connection, and their position will be maintained within the feed-through opening. However, it is also possible to initially mechanically spread the spring element before assembly, thus before the connection of the supply leads to the sensor element, and only then to form the frictional connection by slipping the spring element onto the sensor element and/or inserting the sensor element into the spring element. This permits axe2x80x94at least essentiallyxe2x80x94nearly force-free connection of the sensor element to the supply leads. The xe2x80x9cforce-free connectionxe2x80x9d is referring to the slipping of the spring element onto the sensor element and/or the insertion of the sensor element into the feed-through opening.
Furthermore, another exemplary embodiment of the gas sensor which provides a feature that the feed-through opening has a plurality ofxe2x80x94preferably curve-shapedxe2x80x94depressions running at least essentially in the longitudinal direction of the spring element. The electrically conductive supply leads are pressed by the sensor element into the depressions and are held therein by jamming. This ensures that, after the spring element is mounted, the supply leads are immovably retained in the depressions, thus making it possible to virtually rule out a mutual contacting of the supply leads after the assemblyxe2x80x94at least in the area of the spring element. The number of depressions can be in the range between two and eight. In one especially preferred exemplary embodiment, a total of four depressions are provided in the feed-through opening.
In another exemplary embodiment, the spring element includes a plurality of connectors, each having at least one electrically conductive contact area, to which the supply leads can be attached before or after the spring element is mounted. Understood by attaching is both an integral joining, for example, by a welded connection, as well as a frictional connection, for example, a crimped connection. Because the spring element is fitted with the supply leads before the assembly, the assembly time of the gas sensor can be reduced.
According to another exemplary embodiment, the connectors are inserted into the feed-through opening. The connectors are preferably designed in such a way that in the assembled state of the spring element, a form-locking fit is ensured between the spring element and the connectors. In another exemplary embodiment, the connectors are molded into the spring element, i.e., they are inserted into the ceramic material during the production of the spring element, and are thereby embedded. In both variants of the embodiment, it is possible to spread the supply leads. The isolation of the supply leads in the area of the spring element is effected by the spring element.